Caption: Water quality parameters have been measured in an on-going program by the California Department of Fish and Game in various watersheds in Marin and Sonoma counties from 1991-2002. This graph shows minimum, mean, and maximum water temperature measurements in Ellis Creek, a tributary of the Petaluma River, from 1997-2001. The reference value of 10-15.6°C optimum temperature range for juvenile salmonid rearing is based on McCullough (1999). Maximum water temperatures were in stressful ranges for steelhead trout. See the Info Links for more information.